The problem of correcting for sight defects of the wearer of a respirator is a well known one.
Previous attempts to solve it have concentrated either on providing that the eyepiece of the respirator itself shall be a sight-corrective lens (e.g. CH-A-365948) or that a separate sight-corrective lens shall be added on to the outside of the respirator eyepiece (e.g. U.S. Pat. No. 2,737,659).
The first has the clear disadvantage of the need for customized preparation of complete respirator eyepieces, desirable materials for which, moreover, will not necessarily have the most suitable properties for sight-corrective lenses; the second mainly that the sight-corrective lens will be further away from the eye than would normally be desired, but also that the sight-corrective lens is accessible to damage or dislodgement.
In U.S. Pat. No. Des. 237,757 an eyepiece of a goggle has projecting tabs, presumably for securing it to the straps etc which hold the goggle to the head of the user.